(1) Field of the Invention
The present invention relates to an improved process for the precipitation of aromatic compounds from an aqueous solution using an enzyme. In particular, the present invention relates to a process wherein the enzyme is immobilized on a surface so as to cause the precipitation of the aromatic compound in the solution.
(2) Prior Art
Aromatic organic compounds are found in aqueous solution or suspension in groundwater, in settling ponds associated with public water purification or industrial facilities and in industrial effluents. The latter frequently derive from processes involving the combustion or transformation of fossil fuels, from the forest products industry or from the manufacture of explosives, to name a few of many sources. Aromatic compounds in general are toxic, albeit by a variety of mechanisms, and, therefore, are classed as pollutants.
Existing methods for removal of aromatics from aqueous solution are mainly comprised of physical adsorption onto various media, metabolism by various micro-organisms and chemical combustion in the presence of various oxidants. Each of these methods has some or all of the following drawbacks: (a) time consuming; (b) expensive; (c) ineffective in dealing with pollutants at the levels encountered and/or in reducing pollutant levels to those desired; (d) exhibit a temperature sensitivity (therefore, large seasonal variation); and (e) have a narrow specificity with respect to the classes of aromatic compounds amenable to treatment.
Klibanov has proposed an improvement in which an oxidative enzyme, peroxidase, is added to the aqueous solution to be treated along with the enzyme's co-substrate, hydrogen peroxide. This mixture converts susceptible aromatic compounds to radicals which in a subsequent, presumably non-enzymic, step couple with one another leading eventually to the formation of a precipitate. Susceptible aromatics are hydroxy- and amino-substituted compounds with various other substituents such as alkyl, alkoxy, halo and fused aryl. A series of publications and reports from Klibanov and co-workers describe these findings which are also embodied, in part, in U.S. Pat. No. 4,623,465 to Klibanov. The publications are:
(1) Science, Vol. 221, 259-261 (1983);
(2) Klibanov, National Technical Information Service, PB84-138155, 1-18 (1983);
(3) Detoxication Hazard Waste (Symp, 1981), Edited by J. H. Exner, Ann Arbor Sci. (Publisher) CA 98(12):95130c (1982);
(4) Atlow, et al, Biotechnology and Bioengineering, Vo. XXVi, pp599-603 (1984);
(5) Klibanov, et al, Enzyme and Microbiol. Technol. 3(2), 119-22(1981);
(6) Klibanov, A. M., Enzyme Engineering 6, 3(2), 319-325 (1982); and
(7) Klibanov, A. M., et al., Journal of Applied Biochemistry 2, 414-421 (1980).
The specific improvement claimed in the Klibanov patent is the ability of such a system to effect the clearance of compounds which are not substrates of the enzyme as long as there is a good substrate (a hydroxy- or amino-aromatic compound) also present. An extension is that the clearance of a poor substrate is augmented in the presence of a good substrate. There are, however, aspects to this approach which lower its economic feasibility: (a) it requires large amounts of enzyme because the enzyme appears to be progressively inactivated under the reaction conditions; (b) relatively high concentrations of hydrogen peroxide are employed which are themselves inhibitory to the enzyme; (c) the treatment requires 3 to 24 hours for completion; (d) a final filtration or centrifugation step is required to remove the precipitate generated; and (e) each of the pure compounds studied appears to require removal at a different pH.